Taking the unwinding tension in the diaphragm slitting machine as the research object, a cascade control scheme based on active disturbance rejection control (ADRC) is proposed to address the tension fluctuation problem caused by the nonlinearity, strong coupling, and time-varying parameters of an unwinding system. This cascade control structure can effectively isolate the influence of nonlinear disturbance such as friction of the transmission mechanism on the tension by the inner speed loop with high dynamic performance. The inner speed loop has short control period and high frequency. The extended state observer (ESO) of ADRC is placed in the inner loop, which can effectively reduce the delay of disturbance compensation and further improve the control bandwidth and dynamic performance. The outer tension loop introduces the measures of arranging the transition process of ADRC and nonlinear state error feedback (NLSEF), which effectively alleviates the contradiction between rapidity and overshoot in tension control, and has a good compensation effect on the influence of slow-variable disturbances such as the change of properties of diaphragm and measurement noise of the radius of the unwinding roll on tension. The simulation and experimental results show that the proposed cascade controller has good dynamic performance and anti-interference ability, and can better adapt to the tension control requirements of the diaphragm slitter under different working conditions.